Photographic processes using silver halide have been widely used in the past due to their excellent photographic properties such as sensitivity or control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques capable of easily and quickly providing images have been developed by changing from conventional wet processes using a developing solution to dry development processes, such as processes using heat, etc.
Heat-developable light-sensitive materials are thus well known in this field. Heat-developable light-sensitive materials and processes therefor have been described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553-555 (published by Corona Co., 1979), Eizo Joho (The Image Information), page 40 (April, 1978), Neblette's Handbook of Photography and Reprography, 7th Ed., pages 32-33 (Van Nostrand Reinhold Company), 1977; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777; and Research Disclosure, RD No. 17029, pages 9-15 (June, 1978).
Many different processes for obtaining color image have been proposed. With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,351,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, RD No. 137 pages 31-32 (September, 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Also, processes and materials for forming a positive color image by a light-sensitive silver dye bleach process are described, for example, in Research Disclosure, RD No. 14433, pages 30-32 (April, 1976), ibid., RD No. 15227, pages 14-15 (December, 1976) and U.S. Pat. No. 4,235,957, etc.
Further, processes for forming images upon heat-development utilizing compounds having a dye moiety which are capable of releasing a mobile dye in correspondence or counter-correspondence to the reduction reaction of silver halide to silver under high temperature conditions have been described, for example, in European Pat. Nos. 76,492A and 79,056A, Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83, etc. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".)
With these heat-developable light-sensitive materials, silver salt oxidizing agents are usually employed as suppliers of silver ions. Although such silver salt oxidizing agents are very effective in performance in heat development, they have several disadvantages. Particularly, when the heating temperature is elevated or heating time is prolonged for the purpose of obtaining sufficiently high density, the minimum density (fog density) increases, and a large decrease in sensitivity occurs during preservation before exposure of light-sensitive materials in which a spectrally sensitized silver halide and a silver salt oxidizing agent are coexistent.
Further, it has been desired to shorten the time of development step as much as possible, and thus, investigations on various kinds of development accelerators have been made.